Systems which provide a flow of high pressure hydraulic oil to control the position of a steam turbine valve rack actuator assembly are known. One type of such a system employs separate dedicated hydraulic power unit modules consisting of: a separate reservoir source of hydraulic oil, along with all the necessary oil storage appurtenances; independent power source or sources; separate prime movers to drive the hydraulic pumps; electric motor controls and starters; and oil coolers to maintain the oil systems' temperature. The disadvantages of the dedicated hydraulic power unit modules system are: higher initial capital investment, higher energy consumption, increased maintenance, and a requirement for additional floor space for mounting the hydraulic power unit module.
Another prior art system commonly pressurizes the lubrication supply system pressure to that required of the turbine's valve rack actuator. In such other system, the elevated oil pressure must then be reduced to the pressure of the lubrication oil supply, which is significantly lower than the valve rack actuator oil pressure. The pressure reduction is typically accomplished by a pressure reducing control regulator which converts a large portion of the energy of the higher pressure oil into heat and noise. The disadvantages of this type of system are that it is inefficient and consumes an excessively higher amount of energy, operates at increased noise levels, and requires higher maintenance resulting in reduced equipment life due to continuous higher operating pressures at full flow running conditions.
An example of a system which provides a flow of high pressure hydraulic oil to control the position of a steam turbine valve rack actuator assembly is described in U.S. Pat. No. 2,440,980.